Typical cellular systems divide geographical areas into a plurality of adjoining cells, each cell including a wireless cell site or “base station.” The cell sites operate within a limited radio frequency band and, accordingly, carrier frequencies must be used efficiently to ensure sufficient user capacity in the system.
Call carrying capacity for cellular networks involves the creation of base stations or cell sites across various geographic regions/areas. The base stations/cell sites are partitioned based upon user density/location and, consequently, service providers must purchase real estate and equipment for each site. A base station may provide omni-directional coverage or directional coverage based upon the geography of a particular site. For example, a site may be centrally-located in an open area, void of tall buildings/structures/mountains, such that an omni-directional antenna may be the most efficient arrangement for providing coverage in a particular geographic region. If a mountain range has caused geographic development along one of its sides, then a directional antenna may be best-suited for providing coverage to cellular customers residing on that side of the mountain range. If an area is heavily developed, such as in an urban setting, an antenna which produces a circular, downwardly-directed beam may provide the most efficient cellular coverage for the area. In the case of heavily populated areas, a beam pattern comprising a plurality of lobes may provide the best coverage. Notwithstanding the type of coverage provided by the individual cell sites, one of the more important considerations involves minimizing overlap between adjacent lobes to minimize interference between cell sites.
To improve the quality and reliability of wireless systems, service providers often rely on antenna “diversity” and antenna “polarization.” Diversity improves the ability of an antenna to see an intended signal around natural geographic features of a landscape, including man-made structures such as high-rise buildings. A diversity antenna array helps to increase coverage as well as to overcome fading. Antenna polarization combines pairs of antennas with orthogonal polarizations to improve base station uplink gain. Given the random orientation of a transmitting antenna, when the signal of one diversity-receiving antenna fades due to the receipt of a weak signal, the probability is high that the signal of other diversity-receiving antenna will strengthen. With respect to antenna polarization, most communications systems use vertical, slant and/or circular polarization.
Beam Shaping is another technique employed to optimize call carrying capacity by providing the most available carrier frequencies within demanding geographic environments. Oftentimes user demographics change such that base transceiver stations have insufficient capacity to deal with current local demand within an area. For example, a new housing development within a cell may increase demand within that specific area. Beam shaping can address this problem by distributing the traffic among the transceivers to increase coverage in the demanding geographic sector.
Prior art beam shaping solutions utilize complex beam-forming devices (LPAs, controllable phase shifters, etc.), many of which are not well-suited for deployment atop a masthead or cell tower. A significant design effort involves the use of 2- and 3-sector antennas optimized to provide beam-forming for the purpose of increasing “long term evolution” (4G LTE) data rates in a small cellular network.
Of the various antenna systems employed, Single Input, Single Output (SISO), Single Input, Multiple Output (SIMO), Multiple Input, Single Output, (MISO) and Multiple Input, Multiple Output (MIMO) antenna systems are, by far, the most common. Single Input, Single Output (SISO) antenna are somewhat self-explanatory inasmuch as the antenna employs a single transmitter for sending signals and a single receiver for accepting signals. To multiply the capacity of a radio link, SIMO and MISO telecommunications antennas utilize multiple transmit and/or multiple receive antennas to exploit multipath propagation technology. For example, such technology refers to a practical technique for sending and receiving more than one data signal on the same radio channel at the same time via multipath propagation. Moreover, such telecommunication system are fundamentally different from smart antenna techniques developed to enhance the performance of a single data signal, such as the techniques employed in beamforming and beam diversity.
While telecommunications systems can provide an ability to increase system capacity, the multiple antennas employed therein must be spaced-apart to provide proper isolation between each antenna. Inasmuch as the antenna spacing increases the overall size/diameter of the telecommunications antenna, service providers often impose size constraints which prohibit the type/size of certain antenna. That is, the geometry of a telecommunications antenna is oftentimes too large to fit within the spatial envelope stipulated by the building occupants, residents, service providers, etc.
Furthermore, monopole antennas of the prior art propagate energy in the one-half wavelength (½)(λ) which corresponds to about seven and four-tenth inches (7.4.″) Hence, a full wave-length radiators will be more than about fourteen and eight-tenths inches (14.8″). Since the maximum/desired envelope of certain canister antennas is only about six inches (6.0″), typical low-band radiators are generally dismissed as being too large for such applications.
The foregoing background describes some, but not necessarily all, of the problems, disadvantages and shortcomings related to telecommunications antennas.